When burning a 4 inch diameter glass-jar candle, as the wick burns down, the outer surface edge of candle along jar wall does not get sufficient heat from flame to keep it melted level with center pool.
As wick descends further, often times the wick becomes flooded by wax run-off from outer edge, which is now higher, causing wick to drown itself out. This can happen at different times in a candle's life, but the result is always the same: The center of candle and wick are essentially used up, while a thick ring of wax around the outside edge of candle is left behind, useless, and thus, wasted.
By tamping candle on a regular basis, after extinguishing, while wax is still warm and pliable, a relatively flat surface level can be maintained, thereby preventing wax run-off and eliminating wick flooding.
A candle which is properly maintained from the first burn through the last, at an even surface level, will literally burn itself out, evenly, until all wax is used up in its entirety wasting none.
There will be no thick ring of wax around jar wall, as all wax will have been made to stay at wick's level throughout candle's life. This theory has been tested, many times by inventor, and has proven to be true.
While this device is custom designed to be used with the popular 4 inch diameter glass-jar candles sold at most department stores, the curved edge of its base gives it the versatility needed to be used with various styles and sizes.